Redmine 2.1 / 2.2, translations, etc.

Hello,

Feel free to merge/cherry-pick this set of commits to :
- Mark the plugin as compatible with Redmine 2.2 (tested with 2.2.1, you may want to create a dedicated branch if you wish so).
- Fix an issue with the jQuery code inserting the buttons.
- Make the "PRIVATE" red label available to translators.
- Add Brazilian Portuguese, Turkish and French translations.